Alkyl ketene dimers (AKD) are typically utilized as sizing products in the pulp and paper industry. To this end AKDs, a waxy, water-insoluble substance, are usually added usually in the form of aqueous dispersions comprising cationic starch or cationic synthetic polymers as dispersing agents in the paper making process.
A common procedure used in the preparation of AKD includes the addition of fatty acid chlorides (FAC) (typically having structures of the general formula CH3(CH2)nCOCl where n is an integer ranging from 8 to 20) to a heated mixture of triethylamine (TEA) and an inert solvent(s). Typical processes require the presence of the inert solvent to dilute the above-described slurry to ensure good mixing and product separation. In the absence of the inert solvent, the reaction viscosity of the FAC amine mixture increases as a TEA-Cl salt by-product forms. It is the formation of this by-product in the FAC amine mixture which makes effective mixing of the reactants and removal of the final AKD product difficult to effectively achieve. Examples of typical solvents utilized in the preparation of AKD are propylene dichloride and toluene.
Attempts have been made in the industry to reduce or remove the solvents from the AKD formation process whereby either the dilution solvent has been replaced by an excess amount of tertiary amine or through the use of rigorous distillation. Typically, the resultant AKD is isolated by filtering the solvent/AKD solution where the remaining solvent in the AKD fraction is reduced via distillation. However, such processes, including those utilizing distillation steps, remain problematic because trace amounts of solvent remain in the final product.
U.S. Pat. No. 5,672,721 teaches the production of AKD with low amounts of solvent by using a water immiscible inert solvent followed by a two-stage distillation step followed by the addition of water or steam.
U.S. Pat. No. 5,344,943 teaches a process for the preparation of long-chain alkyl ketene dimers in the absence of additional organic solvents through the use of a molar excess of triethyl amine to fatty acid chloride. The process requires the use of intensive mixing to generate high shear rates which controls the viscosity of the reaction mixture. This process is difficult to practice at the larger scales needed for commercial production of AKD products.
U.S. Pat. No. 5,399,774 teaches the use of tertiary amines as both a reactant and as a diluent. In this use, at least 1.15 moles of amine is used per mole of fatty acid chloride to make AKD. Amines useful in the process may be either monoamines or diamines. The process described teaches stripping tertiary amine hydrogen halide crystals formed in the production of AKD with an acid. Care must be taken when using the acid so as not to hydrolyze the AKD with the acid
U.S. Pat. No. 5,502,218 teaches the solventless production of alkyl ketene dimers which uses pre-prepared crystals of tertiaryamine hydrogen halide as a diluent in the production of AKD products, where the tertiary amines are used in a stoichiometric to molar excess amount relative to the amount of fatty acid chloride used.
There still remains a need to have a process for the manufacture of AKD products which is able to be performed on a commercial scale and which results in a final AKD product which has a sufficiently low level of residual solvent.
The use of solvents in the preparation of AKD creates a problem due to environmental concerns regarding the presence of residual halogenated and/or low boiling solvents in the final AKD product.
These residual solvents pose a problem for the papermaking industry by requiring papermills to make the necessary accommodations for the solvent as it escapes in the exhaust from during drying operations. Also, solvent will be present in effluent produced by the papermills.
Additionally, the residual solvent may be present in the cellulosic products containing the AKD product. The presence of these residual solvents may limit the end uses for these cellulosic products and make their use inappropriate for endproducts which are required to be essentially free of any residual solvents, such as for example for packaging for food contact.
Thus, a heretofore-unaddressed need exists in the industry to provide processes for the preparation of AKD without the addition of solvents which ultimately remain in detectable levels in the final AKD product and cellulosic products treated with AKD products.